feat(feedback): add the Web surface for message feedback

Consume the durable message-feedback sidecar from #2217 in the browser:
per-message Like/Dislike with an optional note, contributed through a
declared assistant-actions slot.

- carry MessageId on finalized AssistantMessageNode so a target is nameable
- declare conversation.chat.assistant-actions and render it in the
  IconActions row between copy and branch
- hold one FeedbackController per Session with per-item ifVersion CAS,
  reconciling a version-conflict from the reply's authoritative item
- mount messageFeedbackRemote alongside goalsRemote

apps/web/tsconfig.json

@@ -53,6 +53,7 @@
     "tests/cordis-tool-round.e2e.ts",
     "tests/web-search-round.e2e.ts",
     "tests/message-actions.e2e.ts",
+    "tests/message-feedback.e2e.ts",
     "tests/markdown-images.e2e.ts",
     "tests/math-rendering.e2e.ts",
     "tests/markdown-cjk-strong.e2e.ts",